Herschel Links Water Around Jupiter to Comet Impact

Astronomers have finally found direct proof that almost all water present in Jupiter's stratosphere, an intermediate atmospheric layer, was delivered by comet Shoemaker-Levy 9, which famously struck the planet in 1994.

The findings, based on new data from the Herschel space observatory, reveal more water in Jupiter's southern hemisphere, where the impacts occurred, than in the north. Herschel is a European Space Agency mission with important NASA participation.

The origin of water in the upper atmospheres of the solar system's giant planets has been debated for almost two decades. Astronomers were quite surprised at the discovery of water in the stratospheres of Jupiter, Saturn, Uranus and Neptune, which dates to observations performed with ESA's Infrared Space Observatory in 1997.

While the source of water in the lower layers of their atmospheres can be explained as internal, the presence of this molecule in their upper atmospheric layers is puzzling due to the scarcity of oxygen there. Its supply must have an external origin. Since then, astronomers have investigated several possible candidates that may have delivered water to these planets, from icy rings and satellites to interplanetary dust particles and cometary impacts.

Data from Herschel's Photodetecting Array Camera and Spectrometer (PACS), with the help of NASA's Infrared Telescope Facility, helped solve the mystery at Jupiter by showing an asymmetry in the distribution of water in its stratosphere, caused by the comet impact. Additional proof for a cometary source for the water came from Hershel's heterodyne instrument for the far infrared (HIFI), which probed the vertical profile of water in the stratosphere. NASA's Jet Propulsion Laboratory in Pasadena, Calif., helped build the HIFI instrument.

"The asymmetry between the two hemispheres suggests that water was delivered during a single event and rules out icy rings or moons as candidate sources," says Thibault Cavalié from the Laboratoire d'Astrophysique de Bordeaux, France, who led the study. "Local sources would provide a steady supply of water, which over time would lead to a hemispherically symmetric distribution in the stratosphere. Depending on whether the chemical species are transported in neutral or ionized form, local sources of water would result in higher concentrations either at the poles or along the equator, but not in a north-south asymmetry."

Hubble Sees a Unique Cluster: One of the Hidden 15

Palomar 2 is part of a set of 15 globulars known as the Palomar clusters. These clusters, as the name suggests, were discovered in survey plates from the first Palomar Observatory Sky Survey in the 1950s, a project that involved some of the most well-known astronomers of the day, including Edwin Hubble. They were discovered quite late because they are so faint -- each is either extremely remote, very heavily hidden behind blankets of dust, or has a very small number of remaining stars.

This particular cluster is unique in more than one way. For one, it is the only globular cluster that we see in this part of the sky, the northern constellation of Auriga (The Charioteer). Globular clusters orbit the center of a galaxy like the Milky Way in the same way that satellites circle around the Earth. This means that they normally lie closer in to the galactic center than we do, and so we almost always see them in the same region of the sky. Palomar 2 is an exception to this, as it is around five times further away from the center of the Milky Way than other clusters. It also lies in the opposite direction -- further out than Earth -- and so it is classed as an "outer halo" globular.

It is also unusual due to its apparent dimness. The cluster is veiled by a mask of dust, dampening the apparent brightness of the stars within it and making it appear as a very faint burst of stars. The stunning NASA/ESA Hubble Space Telescope image shows Palomar 2 in a way that could not be captured from smaller or ground-based telescopes -- some amateur astronomers with large telescopes attempt to observe all of the obscure and well-hidden Palomar 15 as a challenge, to see how many they can pick out from the starry sky.

NASA's Hubble Sees a Horsehead of a Different Color

Astronomers have used NASA's Hubble Space Telescope to photograph the iconic Horsehead Nebula in a new, infrared light to mark the 23rd anniversary of the famous observatory's launch aboard the space shuttle Discovery on April 24, 1990.

Looking like an apparition rising from whitecaps of interstellar foam, the iconic Horsehead Nebula has graced astronomy books ever since its discovery more than a century ago. The nebula is a favorite target for amateur and professional astronomers. It is shadowy in optical light. It appears transparent and ethereal when seen at infrared wavelengths. The rich tapestry of the Horsehead Nebula pops out against the backdrop of Milky Way stars and distant galaxies that easily are visible in infrared light.

Hubble has been producing ground-breaking science for two decades. During that time, it has benefited from a slew of upgrades from space shuttle missions, including the 2009 addition of a new imaging workhorse, the high-resolution Wide Field Camera 3 that took the new portrait of the Horsehead.

The nebula is part of the Orion Molecular Cloud, located about 1,500 light-years away in the constellation Orion. The cloud also contains other well-known objects such as the Great Orion Nebula (M42), the Flame Nebula, and Barnard's Loop. It is one of the nearest and most easily photographed regions in which massive stars are being formed.

In the Hubble image, the backlit wisps along the Horsehead's upper ridge are being illuminated by Sigma Orionis, a young five-star system just out of view. Along the nebula's top ridge, two fledgling stars peek out from their now-exposed nurseries.

Scientists know a harsh ultraviolet glare from one of these bright stars is slowly evaporating the nebula. Gas clouds surrounding the Horsehead already have dissipated, but the tip of the jutting pillar contains a slightly higher density of hydrogen and helium, laced with dust. This casts a shadow that protects material behind it from being stripped away by intense stellar radiation evaporating the hydrogen cloud, and a pillar structure forms.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy Inc., in Washington.

NASA Engineers Review Placement of Webb Telescope's NIRSpec and Microshutters

The installation of equipment into the James Webb Space Telescope requires patience and precision. To prepare for the installation of the actual flight equipment and ensure perfection in the installations, scientists need to practice with an identical test unit. Scientists at NASA's Goddard Space Flight Center in Greenbelt, Md. are currently rehearsing with the placement of the Webb's Microshutter Array into the NIRSpec.

ETUs or engineering test units are simulations of equipment that will fly on the Webb telescope. Back in 2010, NASA Goddard received the ETU of the Webb telescope's Near-Infrared Spectrograph (NIRSpec) instrument from its manufacturer in Germany. Currently, engineers and scientists are preparing and installing the Microshutter Array simulator into the engineering test unit of the Webb telescope's Near-Infrared Spectrograph (NIRSpec) instrument.

"The implementation of a new technology like this depends not only on the conception of it, but it depends on the skilled hands of the engineers and technicians," said Harvey Moseley, a senior astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md. "Using the hundred-fold increase in observing speed provided by the microshutters opens the epoch of the universe where the first galaxies are forming and the elements of our current universe."

NIRSpec will be the principal spectrographic instrument aboard the Webb telescope. A spectrograph is an instrument that separates light into a spectrum. The NIRSpec's components will be sensitive to infrared light from a variety of astronomical objects--from the most distant galaxies in the universe to relatively nearby exoplanets within our Milky Way galaxy. NIRSpec will be capable of obtaining spectra of more than 100 objects in the cosmos simultaneously. Studying an object's spectrum is important, because it helps scientists determine distinct physical properties of the object, such distance, age and even chemical composition. These measurements are important in unraveling the history of galaxy and planet formation.

NIRSpec's Microshutter Array consists of a grid of more than 60,000 microscopic rectangular flaps that act as ‘shutters’ to open or close tiny openings or ‘windows’ for light to pass through. Each individual shutter measures 0.1 by 0.2 millimeters, or approximately the width of a few human hairs. Shutters can be individually addressed and controlled, allowing different ones to be opened or closed in any number of patterns and configurations in order to allow light only from select objects of interest to pass through for dispersion and spectroscopic analysis while rejecting light from other unwanted sources. It is this reconfigurable selectivity of the Microshutter array that enables NIRSpec to look at any field of objects in any part of the sky and do spectroscopy on so many specific objects simultaneously.

Through practice, engineers and scientists will be able to perfect the installation of the Microshutter Array into the NIRSpec. 

The Long and Storied Path to Human Asteroid Exploration

Within NASA’s new FY2014 budget proposal lies a project known as the Asteroid Retrieval and Utilization Mission. This project would be the first to capture a small near-Earth asteroid and safely redirect it to a lunar orbit so that astronauts can visit and explore it. Such a mission would expand scientific knowledge of the origins of both humanity and the universe.

The goal of asteroid retrieval is not a new endeavor for NASA. In fact, the idea dates to the earliest days of the agency. In a 1964 document that looked at “long range future mission planning,” NASA expressed an early aspiration to visit asteroids through unmanned probes by the end of the 1970s. NASA did indeed send a probe through the asteroid belt early in that decade – Pioneer 10 safely traversed the Belt on its way to Jupiter in 1972. By 1969, according to a “Five Year Plan” laid out by the Office of Manned Space Flight, NASA was already looking at plans to send crewed missions to asteroids. However, at the time, the then-latest technology was insufficient to pursue this goal. NASA administrator Robert A. Frosch mentioned this in testimony to Congress on July 29, 1980, when he explained that “a number of evolutionary stages of technology development would be required” for such missions, including “asteroid retrieval to Earth.” Although the capabilities did not yet exist, it is noteworthy that the NASA administrator himself was publicly discussing the idea of asteroid retrieval in 1980. Asteroid retrieval was not just a pipe dream in the minds of a few NASA scientists!

Over the next two decades NASA continued studies and technology development work that would facilitate the capture and exploration of asteroids. In 1992, NASA sponsored a “Near-Earth-Object Interception Workshop” in Los Alamos, New Mexico. At this workshop, those present discussed a “space-based fabrication of very large, microlayer solar sails for asteroid retrieval.” Also discussed was the idea that “such capabilities clearly depend on much expanded human operations in space.” More recently, the International Space Station, has allowed NASA and its international partners to both complete a great deal of research on how to live and work in space, and also to explore long-duration human space flight and its effects on astronauts.

Since the dawn of the new millennium, NASA has also sent several missions to explore asteroids. Multiple probes have completed flybys of asteroids on their way to other planets, and two missions have launched specifically to study asteroids. NEAR (Near Earth Asteroid Rendezvous)-Shoemaker became the first spacecraft to orbit and touch down on an asteroid when it reached the asteroid Eros in 2000 and descended to its surface in 2001, and in July 2011, the Dawn spacecraft became the first probe to enter orbit around an object in the main asteroid belt when it reached the asteroid Vesta. Having completed its investigation of Vesta, Dawn is now on its way to our solar system’s largest asteroid, Ceres.

Thus, NASA’s new Asteroid Retrieval and Utilization Mission is deeply rooted in the storied past of the agency. Thanks to many years of planning and recent technology developments, NASA now has the capability to accelerate current programs that are working on high-powered solar electric propulsion. This, alongside our work on the Space Launch System launch vehicle and the Orion spacecraft, will help us achieve a goal first imagined in the 1960s of retrieving an asteroid for human exploration. 

Blame it on the Rain

A new study tracks the "rain" of charged water particles into the atmosphere of Saturn and finds there is more of it and it falls across larger areas of the planet than previously thought. The study, whose observations were funded by NASA and whose analysis was led by the University of Leicester, England, reveals that the rain influences the composition and temperature structure of parts of Saturn's upper atmosphere. The paper appears in this week's issue of the journal Nature.

“Saturn is the first planet to show significant interaction between its atmosphere and ring system," said James O’Donoghue, the paper's lead author and a postgraduate researcher at Leicester. “The main effect of ring rain is that it acts to 'quench' the ionosphere of Saturn. In other words, this rain severely reduces the electron densities in regions in which it falls."

O’Donoghue explains that the ring's effect on electron densities is important because it explains why, for many decades, observations have shown those densities to be unusually low at certain latitudes on Saturn. The study also helps scientists better understand the origin and evolution of Saturn's ring system and changes in the planet's atmosphere.

"It turns out that a major driver of Saturn's ionospheric environment and climate across vast reaches of the planet are ring particles located some 36,000 miles [60,000 kilometers] overhead," said Kevin Baines, a co-author on the paper, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The ring particles affect both what species of particles are in this part of the atmosphere and where it is warm or cool."

In the early 1980s, images from NASA's Voyager spacecraft showed two to three dark bands on Saturn, and scientists theorized that water could have been showering down into those bands from the rings. Those bands were not seen again until this team observed the planet in near-infrared wavelengths with the W.M Keck Observatory on Mauna Kea, in Hawaii, in April 2011. The effect was difficult to discern because it involves looking for a subtle emission from bright parts of Saturn. It required an instrument like that on Keck, which can split up a large range of light.

The ring rain's effect occurs in Saturn's ionosphere, where charged particles are produced when the otherwise neutral atmosphere is exposed to a flow of energetic particles or solar radiation. When the scientists tracked the pattern of emissions of a particular hydrogen ion with three protons (triatomic hydrogen), they expected to see a uniform planet-wide infrared glow. What they observed instead was a series of light and dark bands – with areas of reduced emission corresponding to water-dense portions of Saturn’s rings and areas of high emission corresponding to gaps in the rings.

They surmised that charged water particles from the planet’s rings were being drawn towards the planet along Saturn's magnetic field lines and were neutralizing the glowing triatomic hydrogen ions. This leaves large “shadows” in what would otherwise be a planet-wide infrared glow. These shadows cover some 30 to 43 percent of the planet's upper atmosphere surface from around 25 to 55 degrees latitude. This is a significantly larger area than suggested by images from NASA’s Voyager mission.

Both Earth and Jupiter have an equatorial region that glows very uniformly. Scientists expected this pattern at Saturn, too, but they instead saw dramatic differences at different latitudes.

"Where Jupiter is glowing evenly across its equatorial regions, Saturn has dark bands where the water is falling in, darkening the ionosphere," said Tom Stallard, a paper co-author at Leicester. "We're now also trying to investigate these features with an instrument on NASA's Cassini spacecraft. If we're successful, Cassini may allow us to view in more detail the way that water is removing ionized particles, such as any changes in the altitude or effects that come with the time of day."

Keck observing time was funded by NASA, with a letter of support from the Cassini mission to Saturn. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency, and the Italian Space Agency. The mission is managed by JPL for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology in Pasadena, Calif.

Suzaku 'Post-mortem' Yields Insight into Kepler's Supernova

An exploding star observed in 1604 by the German astronomer Johannes Kepler held a greater fraction of heavy elements than the sun, according to an analysis of X-ray observations from the Japan-led Suzaku satellite. The findings will help astronomers better understand the diversity of type Ia supernovae, an important class of stellar explosion used in probing the distant universe.

"The composition of the star, its environment, and the mechanism of the explosion may vary considerably among type Ia supernovae," said Sangwook Park, an assistant professor of physics at the University of Texas at Arlington. "By better understanding them, we can fine-tune our knowledge of the universe beyond our galaxy and improve cosmological models that depend on those measurements."

The best way to explore the star's makeup is to perform a kind of post-mortem examination on the shell of hot, rapidly expanding gas produced by the explosion. By identifying specific chemical signatures in the supernova remnant, astronomers can obtain a clearer picture of the composition of the star before it blew up.

"Kepler's supernova is one of the most recent type Ia explosions known in our galaxy, so it represents an essential link to improving our knowledge of these events," said Carles Badenes, an assistant professor of physics and astronomy at the University of Pittsburgh.

Using the Suzaku satellite's X-ray Imaging Spectrometer (XIS), the astronomers observed the remnant of Kepler's supernova in 2009 and 2011. With a total effective XIS exposure of more than two weeks, the X-ray spectrum reveals several faint emission features from highly ionized chromium, manganese and nickel in addition to a bright emission line from iron. The detection of all four elements was crucial for understanding the original star.

"Suzaku's XIS instrument is uniquely suited to this type of study thanks to its excellent energy resolution, high sensitivity and low background noise," said team member Koji Mori, an associate professor of applied physics at the University of Miyazaki, Japan.

Cosmologists regard type Ia supernovae as "standard candles" because they release similar amounts of energy. By comparing this standard to the observed peak brightness of a type Ia supernova, astronomers can pin down its distance. Their similarity stems from the fact that the exploding star is always a compact stellar remnant known as a white dwarf.

Although a white dwarf star is perfectly stable on its own, pair it with another white dwarf or a normal star and the situation eventually may turn volatile. The normal star may transfer gas onto the white dwarf, where it gradually accumulates. Or the orbits of binary white dwarfs may shrink until the two objects merge.

Either way, once a white dwarf begins tipping the scales at around 1.4 times the sun's mass, a supernova soon follows. Somewhere within the white dwarf, carbon nuclei begin merging together, forming heavier elements and releasing a vast amount of energy. This wave of nuclear fusion rapidly propagates throughout the star, ultimately shattering it in a brilliant explosion that can be detected billions of light-years away.

Astronomers can track some details of the white dwarf's composition by determining the abundance of certain trace elements, such as manganese, that formed during the explosion. Specifically, the ratio of manganese to chromium produced by the explosion turns out to be sensitive to the presence of a neutron-rich version of neon, called neon-22. Establishing the star's neon-22 content gives scientists a guide to the abundance of all other elements heavier than helium, which astronomers call "metals."

The findings provide strong evidence that the original white dwarf possessed roughly three times the amount of metals found in the sun. Progressive stellar generations seed interstellar gas with increasing proportions of metals. The remnant, which lies about 23,000 light-years away toward the constellation Ophiuchus, lies much closer to our galaxy's crowded central region than the sun does. There, star formation was probably more rapid and efficient. As a result, the star that blazed forth as Kepler's supernova likely formed out of material that already was enriched with a higher fraction of metals.

Park, Badenes, Mori and their colleagues discuss the findings in a paper scheduled for publication in the April 10 issue of The Astrophysical Journal Letters and now available online.

While the Suzaku results do not directly address which type of binary system triggered the supernova, they indicate that the white dwarf was probably no more than a billion years old when it exploded, or less than a quarter of the sun's current age.

"Theories indicate that the star's age and metal content affect the peak luminosity of type Ia supernovae," Park explained. "Younger stars likely produce brighter explosions than older ones, which is why understanding the spread of ages among type Ia supernovae is so important."

In 2011, astrophysicists from the United States and Australia won the Nobel Prize in physics for the discovery that the expansion of the universe is picking up speed, a conclusion based on measurements of type Ia supernovae. An enigmatic force called dark energy appears to be responsible for this acceleration, and understanding its nature is now a top science goal. Recent findings by the European Space Agency's Planck satellite reveal that dark energy makes up 68 percent of the universe.

Launched on July 10, 2005, Suzaku was developed at the Japanese Institute of Space and Astronautical Science (ISAS), which is part of the Japan Aerospace Exploration Agency (JAXA), in collaboration with NASA and other Japanese and U.S. institutions.

Hubble Sees Light and Dust in a Nearby Starburst Galaxy

Visible as a small, sparkling hook in the dark sky, this beautiful object is known as J082354.96+280621.6, or J082354.96 for short. It is a starburst galaxy, so named because of the incredibly (and unusually) high rate of star formation occurring within it.

One way in which astronomers probe the nature and structure of galaxies like this is by observing the behavior of their dust and gas components; in particular, the Lyman-alpha emission. This occurs when electrons within a hydrogen atom fall from a higher energy level to a lower one, emitting light as they do so. This emission is interesting because this light leaves its host galaxy only after extensive scattering in the nearby gas — meaning that this light can be used as a pretty direct probe of what a galaxy is made up of.

The study of this Lyman-alpha emission is common in very distant galaxies, but now a study named LARS (Lyman Alpha Reference Sample) is investigating the same effect in galaxies that are closer by. Astronomers chose fourteen galaxies, including this one, and used spectroscopy and imaging to see what was happening within them. They found that these Lyman-alpha photons can travel much further if a galaxy has less dust — meaning that we can use this emission to infer how dusty the source galaxy is.

Hubble Sees J 900 Masquerading as a Double Star

The object in this image is Jonckheere 900 or J 900, a planetary nebula — glowing shells of ionized gas pushed out by a dying star. Discovered in the early 1900s by astronomer Robert Jonckheere, the dusty nebula is small but fairly bright, with a relatively evenly spread central region surrounded by soft wispy edges.

Despite the clarity of this Hubble image, the two objects in the picture above can be confusing for observers. J 900’s nearby companion, a faint star in the constellation of Gemini, often causes problems for observers because it is so close to the nebula — when observation conditions are bad, this star seems to merge into J 900, giving it an elongated appearance. Hubble’s position above the Earth’s atmosphere means that this is not an issue for the space telescope.

Astronomers have also mistakenly reported observations of a double star in place of these two objects, as the planetary nebula is quite small and compact.

J 900’s central star is only just visible in this image, and is very faint — fainter than the nebula’s neighbor. The nebula appears to display a bipolar structure, where there are two distinct lobes of material emanating from its center, enclosed by a bright oval disk.